The present invention relates to a light beam scanning device and a light beam scanning lens for use therein.
Light beam scanning devices are widely used in writing optical information and optically reading originals carrying images. There have recently been demands for light beam scanning devices which will find wider use, are less costly, and more compact than conventional light beam scanning devices. For making a light beam scanning device compact, it is effective to employ a wider-angle light beam scanning lens in the device. For manufacturing a light beam scanning device, it is effective to employ a single-element light beam scanning lens in the device.
The applicant has proposed an f.theta. lens as a light beam scanning lens for use with parallel rays of light (see Japanese Laid-Open Patent Publication No. 61-48684). The proposed f.theta. lens is a single-element lens, and has a curvature of field in the range of from 5 to 10 mm at a half field angle of about 21.degree. with respect to f=300 mm. Since this lens is not suitable for use as an ultrawide angle lens, it poses a certain limitation on efforts to make light beam scanning devices compact.
Japanese Laid-Open Patent Publication No. 54-87540 discloses a single-element lens for use as a light beam scanning lens, the lens having a function similar to an f.theta. function with respect to a divergent deflected light beam applied thereto. This lens also has a curvature of field of more than 5 mm at a half field angle ranging from 15.degree. to 17.degree. with respect to f=150 mm. The lens is also not suitable for use as an ultrawide angle lens, and cannot make light beam scanning devices appreciably compact.